This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Single-walled carbon nanotubes are molecular wires that exhibit interesting structural, electrochemical, and optical properties. The near-infrared optical absorption properties of polymer- and biomaterial-functionalized single-walled carbon nanotubes have attracted particular attention for optical nanobiosensors. Deoxyribonucleic acids (DNAs) play important physiological and pathological roles in living organisms. The unique structural properties of single-walled carbon nanotubes make them extremely useful as a carrier of macromolecular enzymes and DNAs. Optical properties of DNA-functionalized single-walled carbon nanotubes are sensitive to many chemical and biological materials such as hydrogen peroxide, glucose, protein, oxygen, ammonia, and ascorbic acid. This provides us with useful approaches to develop optical biomedical sensing applications. Hydrogen peroxide is one of the main products for many enzyme-catalyzed chemical reactions. The over accumulation of hydrogen peroxide in living systems is related to aging and severe diseases. It has been found that the linear optical absorption properties of DNA[unreadable]functionalized carbon nanotubes in the near-infrared range significantly depend on the concentration of hydrogen peroxide. This proposed program concentrates on nonlinear optical absorption properties of double-stranded DNA-functionalized carbon nanotubes. We will use a nanosecond pulsed near-infrared laser system and employ the open aperture Z-san technique to characterize nonlinear optical absorption coefficient of the dispersions of double-stranded DNA-functionalized carbon nanotubes under different concentrations of hydrogen peroxide to determine the relation between the nonlinear optical absorption coefficient and the concentration of hydrogen peroxide. This research can be extended from the dispersions to the thin films of double-stranded DNA-functionalized carbon nanotubes during the academic year. The results will reinforce the potential of double-stranded DNA-functionalized carbon nanotubes for use in optical biosensing.